AU601985B2

AU601985B2 - Method and device for the mechanical control of building works

Info

Publication number: AU601985B2
Application number: AU74374/87A
Authority: AU
Inventors: Jean Paquet
Original assignee: RECH BATIMENT TRAVAUX PUB
Current assignee: Centre Experimental de Recherche et dEtudes du Batiment et des Travaux Publics CEBTP
Priority date: 1986-05-21
Filing date: 1987-05-21
Publication date: 1990-09-27
Anticipated expiration: 2007-05-21
Also published as: US4881405A; AU7437487A; FR2599150B1; FR2599150A1; WO1987007378A1; GB2199662A; GB2199662B; GB8801075D0

Description

-AU-AI-74374/87 O~~RGANISATION MNILDELA PROPRIET ITELL rU DEMANDE INTERNA\TIONALE PUBLIEE EN VRI TILC ERQO MATIERE DE BREVETS (PCT) (51) Classification interlitionale des brevets 4 I (11) Num~ro de publication internationale: WO 87/ 07378 G01N 3/30,29/04 Al (43) Date de publication internationale: 3 d&c embre 1987 (03,12.87) (21) Numiro de la demande internationale: PCT/FR87/00 177 (22) Date, de dip6t international: (31) Num~ro de la du~mande prioritaire (32) Date de priorit6: (33) Pays de priorit6: 21 mai 1987 (2 1.05.87) 86/67234 21 mai t986 (2 1.05.86) (81) Etats disignis: AU, GB, US, Publje Avec rapport de rechierchze internationale.

A Y'ant lexpiration dui d~Iai pr~vu pour la mnodification des revendicauions, sera republi~e si de telles miod (fica- (ions sont recues.

(71) D~posant (pour t'ous les Etats d~sign~s sau* US): CEN- TRE EXPERIMENTAL DE RECHERCHES ET D'ETUDES DU BATIMENT ET DES TRAVAUX PUBLICS [FR/FR]; 12, rue Brancion, F-75737 Paris C~dex 15 (FR).

(72) Inventeur; et Inventeur/Diposant (US settlement) PAQUET, Jean [FR/FR]; 13, rue Corot, Domaine des G~itines, F- 78370 Plaisir (FR).

(74) Mandataire: MARTIN, Jean-Jac,, 4 es; Cabinet Regimbeau, 26, avenue K161- r, F-75116 Paris (FR).

This document contains the u~~dmnts made under ,ept~it,'n49 and is correct for prim ing.

A.O0i4p, 4 FEB 1988

FAUSTRALIAN

2 2 DEC 1987 PATENT OFFICE (54)Title: METHOD AND DEVICE FOP, TAIE MECHANICAL CONTROL OF BUILDING WORKS (54)Titre: PROCEDE ET DISPOSITIF DE CONTROLE MECANIQUE DE REVETEMENTS D'OUVRAGES (57) Abqtract The method comprises the determination of at least one signature (2a) of the response to an impulse shock of a sound reference coating or covering, and a plurz,!-.ty (2b-2i) of' signatures of the response of an, impulse shock to a covering having sample defects in order to establish reference signatures.. The covering to be controlled is sub; ected at a plurality of test points (Pi) to at least ont Impulse shock test in order to determine the corresponding measurement signatures (MSi). A comparison of the measurement signatures with the reference signatures makes it possible to identify defects by resemblance criteria.

Application to the control of coatings of traffic roads such as motorwvays for motor vehicles and runways for aircraft.

(57) Abril;6 .j-t I Ins] Lxmr Le procWd6 consiste Ak 6tablir au momns une signaturet(2a) de Ia r~ponse A un choc irnpulsionnel d'un rev~tement sain, de ri~f6reace, et une pluralit6 (2b A 2i) de signature de la r~p~nse d?-u choc impulsionnel d'un rev~tement muni de d~ft'uts d'6chantillons pour constituer des signatures de r~f~rence. Le revdtement A contr6ler est soumis'eii tii'~ pluralit6 de de test A au momns un test de choc impulsionnel pour determiner des signatures de mesure (MSi) correspond~ntl,. Une comparaison des signatures de mesure aux signatures de r~f~rence permet d'~tnblir une identification des d~fpb'i par critire de ressemblance., Application au contr6le de revetements de voles de cireulatlon, telles que autoroutes istes d'envol d'a~ronefs.

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WO 87/07378 PCT/FR87/00177 1 METHOD AND DEVICE FOR MECHANICA' TESTING OF CIVIL ENGINEERING STRUCTUiRE SURFACINGS The present invention relates to a method and device for mechanical testing of civil engineering structure surfacings.

At present the mechanical testing of the surfacings of civil engineering structures such as pathn, roads, motorways and runways for aircraft remains somewhat unsatisfactory. Such structures can have defects due to their construction or defects resulting from subsequent damage due to movement of the soil or subsoil, especially in the case of paths. In the particular case where the surfacings consist of concrete slabs cast in situ with or without a metal reinforcing e* 15 grid the constructional defects previously mentioned can "00 include clumps of aggregate and voids due to the reinforcing grid, for example. Subsequent damage results in particular from relative movement between the surfacing and the underlying layers of soil or subsoil; in the case of concrete slabs forming the surface surfacing of motorways, damage results in particular from the phenomenon of pounding of the slabs due to the circulation of vehicles, decompacting of the underlying soil resulting in the creation of voids. The testing methods proposed until now essentially comprise mechanical testing methods using vibrating rollers and electromagnetic methods using georadar.

The aforementioned mechanical testing methods consist in subjecting the surfacing to mechanical vibration at a fixed frequency and measuring the amplitude of the corresponding vibrations. The mechanical vibrations employed are produced by a roller vibrating at a frequency between 10 and 20 Hz.

Although the difficult problem of sensing the response of the surfacing has been solved in a WO 87/07378 PCT/FR87/00177 f 2 satisfactory way through the use of a hydrophone wheel, there is no way that the aforementioned response can be regarded as providing comprehensive information on the mechanical state of the surfacing and of the interfaces between it and the soil, given the incomplete nature of the spectrum of frequencies generated by the vibrating roller.

Electromagnetic testing methods using high-frequency electromagnetic waves involve detecting reflections of the electromagnetic waves emitted from structural discontinuities in the surfacing or from its interfaces with the soil. However, given the nature of the waves transmitted, not all material discontinuities in the surfacing or in its interfaces will necessarily produce interference by reflection that can be measured in a reliable way, and interpreting the measurement cS results is extremely difficult. Also, and by virtue of o;ff the nature of the waves employed, the measurement results are highly sensitive to the moistute content of the surfacing and its interfaces and to the presence in the surfacing or in the underlying layers of metal materials.

S One object of the method and device for mechanical testing of civil engineering structure surfacings in accordance with the invention is to remedy the aforementioned disadvantages, une inherent disadvantages of both the prior art methods in particular being eliminated.

Another object of the present invention is the provision of a method and a device for mechanical testing of civil engineering structure surfacings in which the surfacing is subjected to mechanical vibration in a wide frequency spectrum.

Another object of the present invention is to provide a method and a device for mechanical testing of L 1_ 1 l

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00 S 0 0@0* civil engineering structure surfacings that can be implemented on a quasi-automatic basis.

AnO ther object of the present invention is to provide a nethod and device for mechanical testing of civil engineering structure surfacings in which the probability and reliability of detection arr high.

The method in accordance with the invention for mechanical testing of civil engineering structure surfacings is remarkable in that it consists in establishing at least one signature of the response to an impulse impact of a reference sound surfacing and a plurality of signatures of the response to an impulse impact of a same type surfacing in which reference sample faults have been produced, the aforementioned 15 signatures constituting reference signatures. A plurality of points on the surfacing under test are subjected to at least one impulse impact test so as to determine the so-called measurement signature of the impulse response at each of the specific points. The 20 measurement signatures are compared with the refererence signatures to establish an identification based on criteria of resemblance.

The device in accordance with the invention for mechanical testing of civil engineering structure 25 surfacings is remarkable in that it comprises a mobile support adapted to be moved over the surfacing.

Percussion means disposed on this support make it possible to generate sequentially calibrated test impacts on the surface. Sensing means fastened to the mobile support but mechanically decoupled from it serve to deliver an electrical signal representative of the impulse response of the surfacing to the calibrated test impacts.

The method and the device in accordance with the invention are applicable to the mechanical testing of ii 1 WO 87/07378 PCT/FR87/00177 4 civil engineering structure surfacings of all kinds and in particular paths such as roads, motorways and runways for aircraft, for example.

Their object will be better understood from a reading of the following description and reference to the accompanying drawings in which: figure 1 represents the topography whereby various sample defects are laid out over a reference test area, figures 2a through 2i respectively show the nature of the surfacing, with or without a sample defect, and the corresponding reference signature constituted by the impulse response of the corresponding reference point in question.

figure 3 shows amplitude-time and amplitudefrequency curves for a calibrated impact in accordance S. with the present invention, figure 4 shows a block diagram of a processor for applying the choice criteria of the method in accordance with the invention, figure 5 is a diagram illustrating the implementation of the method in accordance with the invention, figure 6 is a schematic plan view of a device in accordance with the invention, figures 7a and 7b show a detail of the device as shown in figure 6 and figure 7c shows a timing diagram for various component parts from figures 7a and 7b, 30 figures 8 and 9 respectively show a particularly advantageous embodiment of an essential part of the device and the device in accordance with the invention.

The method in accordance with the invention for mechanical testing of civil engineering structure t WO~~ ifLV37 PC/F8700 woU i/07378 PCT/FR87/00177 r 1 surfacings will first be described with reference to figures 1 and 2.

By civil engineering structures there is meant, of course, any structure in the civil engineering domain and in particular, but not in any limiting way, any surfacing of paths such as roads, motorways and runways for aircraft.

The method in accordance with the invention for mechanical testing of civil engineering structure surfacings consists in establishing at least one signature of the response of a reference sound surfacing to an impulse impact. A plurality of signatures of the response of a surfacing of a surfacing of the same type to an impulse impact is then established, for a 15 surfacing in which reference sample defects have been formed. The signatures relating to the reference sound surfacings and to the surfacings comprising sample defects constitute reference signatures.

Figure 1 shows a reference test area indicating 20 the topography according to which the various sample defects have been laid out. The test area may thus correspond to a particular surface area and, in the particular case of motorway surfacings made up from concrete slabs of standardized dimensions, one of these 25 slabs. A signature of the response to an impulse impact for a reference sound surfacing, the area denoted S in figure 1, is shown in figure 2a. In the same way there is established a plurality of signatures respectively shown in figures 2b through 2i of the response of a e *e 30 surfacing of the same type in which various reference sample defects have been formed to an impulse impact.

In figure 2b the defect corresponding to area 1 in figure 1 corresponds to a box situated at the bottom of the surfacing, that is to say above the foundation supporting the latter and corresponding t\o a void WO 87/07B,78 PCT/FR87/00177 I I *00

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approximately 2 cm thick. Likewise, the sample defect introduced in the area 2 in figure 1 corresponds to a clump of aggregate caused by segregation of the latter, which separate out from the cement grouting constituting the concrete while the latter is being cast. The corresponding signature is shown in figure 2c. Figure 2d shows the signature of a sample defect situated in area 3 of the reference area shown in figure 1, this sample defect consisting of a box disposed near the surface of the surfacing and corresponding to a void 2 to 3 cm thick. Note in this case the very strong increase in the offset of the signature, this increase actually necessitating a reduction of scale to enable it to be represented properly. Likewise, the sample defect 15 introduced in area 4 of the reference test area shown in figure 1 corresponds to an inclined box with a void thickness of approximately 2 cm, the corresponding signature being shown in figure 2e. Once again, note the very high variation in the offset of the corresponding signature relative to a sound concrete surfacing as shown in figure 2a, for example. The sample defect in area 5 of the reference test area shown in figure 1 corresponds to a box disposed near the surface of the surfacing, this box corresponding to a void thickness of approximately 1 cm. The corresponding signature is shown in figure 2f. The signature shown in figure 2g corresponds to a clump of stones situated near the interface between the surfacing and the foundation.

A change in the average offset of the corresponding signature will be noted in this figure. The sample defect corresponding to the signature of figure 2g is situated in area 6 of the reference area shown in figure 1. The sample defect in area 7 of this same reference area corresponds to a defect comparable with the sample defect in area 6, but in which the stones are larger.

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i~ ~A U _r WO 87/07378 PCT/FR87/00177 7 The signature corresponding to the sample defect of area 7 is shown in figure 2h. In this latter case there will again be noted a slight variation of the offset of the corresponding signature, followed by a signficant increase in this same offset. Finally, the signature shown in figure 2i corresponds to a defect in area 8, where there is no deliberate sample defect, an abnormally high mechanical admittance appearing in the aforementioned area. The corresponding signature is shown in figure 2i and in this figure a substantially constant value of the average offset of the signature will be noted.

Using the method in accordance with the invention, the surfacing under test is subjected at a 15 plurality of specific points thereon denoted Pi to at least one impulse impact test so as to determine the so-called measurement signature denoted SMi of the impulse response at each of the aforementioned points Pi. As seen in figure 2 in particular, but in a 20 non-limiting way, the reference signatures shown at 2a through 2i and the measurement signatures SMi are responses to an impact pulse in a mobility-frequency v..e diagram. The reader is reminded that the mobility at eg\\ the test points Pi considered is the ratio of the speed 25 at the measurement point to the force of the impact applied to it. Other parameters such as the acceleration at this point may of course be used, in a non-limiting way. Thus, as shown in figures 2a through 2i, the mobility-frequency diagrams are graduated in frequency along the abscissa axis and in mechanical admittance along the ordinate axis, the mobility being assumed as representative of the mechanical admittance at the measurement point in question. Using the mechanical testing method in accordance with the invention, the impact pulses used to establish the

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t- WO 87/07378 PCT/FR87/00177 reference and measurement signatures are calibrated impact pulses. To give a non-limiting example, as shown in figure 3, the calibrated impact pulses may advantageously consist in an impact pulse having a duration less than 1 ms and a peak amplitude greater than 100 daN, for example. The amplitude-time diagram for the corresponding calibrated impact pulse is shown in figure 3a, figure 3b showing the distribution of energy as a function of frequency for the calibrated pulses. The distribution of energy as a function of frequency for t'he calibrated impact pulses is such that the energy corresponding to a frequency in the order of 2 kHz is greater than one tenth of the maximal energy at low frequencies, for example.

In an advantageous embodiment of the method in accordance with the invention said measurement signatures are compared with the reference signatures, in a non-limiting way, by comparing specific values from e the mobility-frequency diagram for the measurement 20 signatures, denoted SMi, with corresponding values referred to as inherent values of the reference signatures previously shown in figures 2a through 2i.

The aforementioned identification may then be arrived at by calculating a coefficient of correlation or of 25 resemblance between the reference signatures and the measurement signatures.

A particularly advantageous example of such calculation will now be described with reference to S. 30 figure 4.

Referring to this figure, the signals representing the amplitude of the impact pulses denoted F and those representing the speed or acceleration at the test point Pi are sensed as a function of time beginning from the reference time, for oxample. These signals, after conversion into digital signals, for L WO- B 7 r

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n WO 8:7/07378 PCT/FR87/00177 9 example, are then respectively submitted in steps A and B to fast Fourier transform processing for a specific number of points. In an advantageous embodiment of the method in accordance with the invention, the fast Fourier transform may be applied to 512 samples or values. In the case of the signal representing the speed or acceleration at the test point Pi in question, the signal is pre-emphasised by filtering it before it is subject to the fast Fourier transform processing.

The values obtained are then subjected to the processing denoted C in figure 4 which makes it possible to establish for certain specific frequency bands the amplitude-phase relationship between the values obtained from the fast Fourier transform processing in the 15 preceding steps A and B. The aforementioned amplitudephase values in fact correspond to the ratio of complex values for the speed at the test point Pi in question to the corresponding impact amplitude for the frequency band in question. A second stage of processing may then 20 be applied in the step marked B in figure 4 in such a way as to determine the corresponding energy in each frequency band considered. The results obtained in this way may be combined in a final step E which makes it 2 possible, for example, to define energy values in the 25 frequency bands considered related to a plurality of frequencies referred to as inherent values in the case of the reference signatures, for example. Of course, analogue processing is effected relative to the signals constituting the measurement signatures at each test 30 point Pi. Correlation with a view to establishing the criteria of choice is then effected between the values corresponding to the inherent values of the reference signatures and of the measurement signatures. The mathematical method for processing the values as employed in the method in accordance with the invention 87077 PC/R70 7 WO 87/07378 PCT/FR87/00177 will not be described in more detail, being specified by way of non-limiting example only.

According to one advantageous characteristic of the method in accordance with the invention, the previously determined points designated Pi at which the surfacing is subject to at least one impulse impact test may advantageously be distributed in a meshed array, the array increment r being determined according to the resolution required. Figure 5 shows a array of points of this kind, the points previously designated Pi being now designated with the general reference letters Pij, in such a way as to constitute the mesh of a array. In a non-limiting way, the array shown in figure corresponds to a array in which the increment is exactly 15 the same in two directions at right angles. Of course the increment in these two dimensions or directions may

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:6 be chosen differently, according to the required application. Measurements carried out using the method in accordance with the invention have made it possible, using a array with an increment r of 1 metre, to obtain a resolution of better than 30 cm. Of course, reducing the array increment makes it possible to increase the resolution required of the system. Establishing measurement signatures denoted SMij relative to each S 25 point Pij of the array then makes it possible to establish a true map of the surfacing and of the mechanical structure of the interfaces between the surfacing and the foundation supporting it.

S* A detailled description of a device in e 30 accordance with the invention for mechanical testing of civil engineering structure surfacings enabling implementation of the method in accordance with the invention as previously described will be given with reference to figures 6 through 9.

Referring to figure 6, the device in accordance i Wa 87038PT/R 007 WO 87/07378 PCT/FR87/00177 I 4

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66i *S 11 with the invention comprises a mobile support denoted 3 that can be moved in a direction denoted T in the aforementioned figure 6 over the surface of the surfacing to be tested. It will be noted, for example, that the mobile support 3 is fastened to a carriage denoted 1 provided with wheels, for example, which is itself towed by an automobile vehicle denoted 2 during implementation of the method. The support 3 may be rendered mobile relative to the surfacing by any means, of course, depending on the application of the method and the device in accordance with the invention.

Percussion means denoted Mi are disposed on the support 3, these means making it possible to generate sequentially on said surface of the surfacing to be tested calibrated test impacts. Also, sensor means denoted Ci are fastened to the mobile support, these sensor means being mechanically decoupled from the support 3. By mechanical decoupling is meant any means of obtaining maximum attenuation of any mechanical vibration due to displacement of the support 3 relative to the surface of the surfacing for the aforementioned sensor means Ci. Thus, given the previously described mechanical decoupling, the sensor means Ci are able to deliver an electrical signal representat ve of the impulse response of the 'facing at the test point P? considered to the calibrated test impact generatd by the percussion means Mi As seen also in figure 6, the percusaion means Ci are advantageously constituted by a plurality oi percussion members aligned in a direction S on the mobile support 3. The percussion members Mi and the sensor means Ci may advantageously be adjustable in relative position in the alignment direction As also seen in figure 6, with each percussion member Mi is associated a sensor member Ci, the set? F 4 6 6050 *c S 6g 0 0 *060, 4 r 0 WO 87/07378 PCT/FR87/00177 12 sensor members constituting the previously described sensor means. In a non-limiting way, each group constituted by a percussion member Mi and a sensor member Ci may of course be adjustable in translation along the alignment direction S Thus installation of the percussion members Mi and their associated Sensors Ci with a predetermined increment makes it possible for a particular dispacement of the mobile support 3 in the translation direction T to generate the array of test points Pij previously described in figure 5. As already mentioned, the array may be a square or rectangular array. According to one characteristic of the device in accordance with the invention for testing civil engineering structure surfacings, the distance 15 separating a percussion member Mi from the corresponding sensor memoer Ci associated with it preferably does not exceed 10 cm, A more detailed description of the percussion o. members Mi will now be given with reference to figures 20 7a and 7b in particular.

Referring to figure 7a, which shows a plan view of a particular percussion member Mi, each of these members comprises a percussion head denoted 14, mounted at the ena of an arm denoted 6 forming a lever 25 arm. The arm 6 forming a lever arm is rotatable about a shaft denoted 7 in figures 7a and 7b, susbstantially parallel to the alignment direction Drive means 8, 9, 10 for the arm 6 make it possible through the intermediary of the percussion head 14, 15 to generate a plurality of successive calibrated impacts as previously defined. The calibrated impacts may, as previously mentioned, consist in an impact pulse with an amplitude between 100 and 1000 dai and a duration less than or equal to 1 ms.

As seen also in figures 7a and 7b, the WO 87077 PCT/ER7/001 WO 87/07;378 PCT/FK87/0177 I I 13 electromechanical clutch coupling device denoted 8, 9 is mechanically fastened to the arm 6 forming the lever arm. The electromagnetic clutch coupling device may be a device available through normal trade channels, for example, in particular an electromagnetic clutch coupling device distributed by the company BINDER MAGNETIC. Drive means denoted 10, 11, 12 serve to rotate said clutch, the drive means consisting of a motor-gearbox unit, for example. The rotational drive means 11, 12 and the clutch coupling device 8, 9 serve to displace the arm forming the lever arm 6 and the percussion head 14, 15 into a calibrated impact armed position. This calibrated impact armed position of the percussion head 14, 15 and of the arm 6 is denoted I in 15 figuro 7b.

fo As will be noted also in figures 7a and 7b, return spring means 13 mechanically fastened to the support 3 for example and to the arm forming the lever arm 6 are also provided. The return spring means 13 and the clutch coupling device 8, 9 make it possible to displace the arm forming the lever arm 6 and the percussion head 14, 15 into the calibrated impact position. In figure 7b in particular the calibrated impact position is denoted II.

A timing diagram for the functioning of the various component parts of each percussion member Mi shown in figures ia and 7b will be given with reference to figure 7c.

In figure 7c there is shown at 1 a control pulse lelivered by a reference clock or control sequencer, at 2 the corresponding control signal for the drive means 11, 12 constituted by the motor-gearbox unit of figure 7a, at 3 the corresponding timi ,g diagram for an end of travel limit switch on the shaft of the previously described motor-gearbox unit, at 4 the corresponding WO 87/07378 PCT/FR87/00177 WOj 87/07378 PCT/FR87/00177 114 14 active and passive phases of the electromagnetic clutch coupling device 8, 9 and, finally, at 5 the armed and calibrated impact positions denoted I and II, in conformity with figure 7b, of the percussion head 14, and the lever arm 6. It will be understood that in the previously mentioned figure 7c the active position of the electromagnetic clutch coupling device 8, 9 makes it possible to displace into and/or maintain in the calibrated impact armed position the percussion head 14, 15 and the lever arm 6 whereas the passive positi.on of the latter enaoles the movement to the calibrated impact position denoted II. Also, the return of the electromagnetic clutch coupling device 8, 9 to the active position, as seen in figure 7c, makes it possible to S. 15 capture the combination constituted by the lever arm 6 S. and the percussion head 14, 15 so as to prevent, in accordance with the invention, any rebound after a given calibrated impact. The sequential triggering of each of .the percussion members Mi naturally x. 'es it possible to generate in succession a plurality of calibrated impacts. The calibrated impacts may advantageously be generated at different points Pi or a plurality of 0,0. calibrated impacts may be generated at the same point in order to obtain a plurality of values in order to determine average values. According to a specific characteristic of the device in accordance with the invention, the duration of the passive phase of the electromagnetic clutch coupling device 8, 9 previously described may be adjustable so as to achieve by adjusting this duration calibrated impacts without any rebound. This duration is determined experimentally according to the modulus of elasticity of the material of the percussion head 14 ,And the hardness of the surfacing. To givq a non-limiting example, the percussion head 14 rmy be constituted by a v4 1'.

WO 8 7 WO 87/0)7378 PCT/FR87/00177 superpolyamide plastics material such as the materials raarketed by the company ERTA under the trade name EKTALON. A plastics material will preferably be chosen with a modulus of elasticity between 90 000 and 170 000 N/cm 2 The percussion head 14 may advantageously comprise a spherical dome-shaped percussion surface, the latter having a radius of curvature in the order of 20 cm, for example.

A more detailled description -f the sensor means Ci associated with the percussion means Mi will now be given with reference to figure 8. The aforementioned figure represents a cutaway view of one particularly advantageous embodiment of the sensor means Ci showing the internal arrangement of the latter.

15 Referring to this figure, the sensor means Ci comprise a box 16 forming a chassis for the sensor S S* means. In operation the box 16 is rendered mechanically Sfast with the mobile support 3 or with a support 19 fastened to the latter, through the intermediary of first decoupling spring means 18. As shown in figure 8, the box 16 or chassis is, depending on its non-functional or functional status, respectively rendered fast or not with the support 19 or 3, through the intermediary of a system comprising an actuator 25, a piston rod 26 and a ring 28 which make it possible to move the box 16 into contact with the support 19 when the latter is not operational, or, on the contrary, the rod 26 being disengaged from the ring 28, to render the 'box 16 fast with the mobile support 3 (19) through the intermediary only of the first decoupling spring means 18 when the sensor means Ci 4 n question are operational.

The sensor means Ci shown in figure 8 further comprise a sensing head 20, 21, 22, 23 mechanically fastened to the box forming the chassis 16 through the intermediary of seC ind decoupling spring means 24. As seen also in il WO 87/07378 PCT/FR87/00177 16 figure 8, the sensing head may advantageously comprise a support lever arm 22 pivotting in rotation about a fixed shaft denoted 220 relative to the chassis 16. The opposite end of the lever arm 22 is mechanically fastened to the chassis 16 through the intermediary of the second decoupling means 24. The sensing head further comprises a sensing cell 20, 21 mechanically fastened to the lever arm 22 through the intermediary of third decoupling spring means 23. In an advantageous embodiment the sensing cell 20, 21 may comprise an electromechanical transducer 20 of the accelerometer or geophone type. The sensitive surface of the transducer is mechanically fastened to a spike 21 made from a hard material adapted to be placed in contact with the t 15 measurement point Tn1 the surface of the surfacing.

3' AccelArometers tE constitute acceleration sensors with a frequency bandwidth substantially between C and 10 000 Hz. Geophones, on the other hand, constitute speed sensors with a bandwidth substantially between 4 Hz and 5 000 Hz. The spike 21 may itself be made from very hard steel and the force with which the spike bears on the surfacing may, to give a non-limiting example, be equal to 1 Newton in the case where the electromechanical transducer is an accelerometer with a mass of 2 grammes or 10 to 20 Newtons in the case where the electromechnical transducer is a geophone with a mass in the order of 20 g. The radius of curvature of the spike 21 may be in the order of a few millimetres.

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nThus, given the structure of each of the sensors Ci as shown in figure 8, the latter jointly serve to establish a force with which the spike 21 bears on the surfacing through the intermediary of the first, second and third decoupling spring means in particular with appropriate vibrational decoupling, the third decoupling means 23 having the effect in particular of mechanically WO 87/07378 PCT/FR87/00177 I I decoupling the sensing cell 20, 21 and the lever arm 22 by increasing the bandwidth at high frequencies, the only mass as seen by the Spike 21 at these frequencies being the mass of the spike plus that of the geophone but virtually none of that of the arm 22. In order to seat the box 16 forming the chassis on the surfacing under test during operation, it comprises as seen in figure 8 three support spikes 17 adapted to come into contact with the latter surface. Thus, given the inherent structure of each of the sensing means Ci shovi in figure 8, and in particular given the presence of the first, second and third decoupling means previously described, the force with which the box 16 is applied to the surfacing through the intermediary of the spikes 17 15 is determined only by the first decoupling means 18 whereas the force with which the spike 21 is pressed o* into contact with the measurement point is determined only by the lever system 22, second decoupling means 24 and third decoupling means 23. Laboratory tests comparing a sensor directly stuck in the vicinity of a test point 11i and sensor means Ci as shown in figure 8 have shown a very high degree of similarity of the response characteristics.

A more detailled description of the architecture S 25 of the device in accordance with the invention for mechanical test of civil engineering structure surfacings fron, .e point of view of its functional arrangement will now be given with reference to figure 9.

As -een in this figure, the device advantageously further comprises processor means for sequential control of the device and processor means for processing the reference and measurement signatures according to the method in accordance with the invention as previously described.

WO 87/07378 PCT/FR87/00177 18 The control processor and calculation means advantageously comprise a microcomputer provided with peripheral devices. To give a non-limiting example, the peripheral devices may comprise a control keyboard denoted KL and a display monitor denoted MO. The microcomputer is symbolically represented by its central processor unit denoted UC. The peripheral devices of the microcomputer may further comprise non-volatile memory means used to memorise digital values representative of the measurement signatures. The aforementioned non-volatile memory means may comprise, for example, a magnetic hard disk HD, given the very large number of measurements to be carried out, given the large number of test points. The peripheral devices 15 of the microcomputer may advantageously further comprise no electrically reprogrammable (EEPROM) type memory means in which are memorised digital values representative of I the so-called reference signatures. These, after they are established on a reference test area as previously described with reference to figure 1, may be memorised and, where necessary, modified because of specific experimental or utilisation circumstances. Finally, the peripheral devices of the microcomputer may comprise reprogammable read-only (REPROM) type memory means in which there is memorised a program for calculating and processing values in order to compare the signatures SMi with the reference signatures 2a through 2i to establish an identification on the basis of resemblance criteria as already described previously in this description.

Finally, the control processor means comprise control interfaces denoted IF, analogue-digital/ digital-analogue input/output interfaces connected to the drive members and the control members of the percussion members Mi and the sensor means Ci. These control interfaces will not. be described in that they r i I i i WO 87/07378 PCT/FR87/00177 19 may be constituted by any means available tirough normal commercial channels.

In an advantageous embodiment of the device in accordance with the invention for mechanical testing of civil engineering structure surfacings, the previously described input/output control interface means IF may advantageously comprise a sensjr responsive to the peak value of the amplitude of the calibrated impact generated by a percussion means Mi. This peak value sensor delivers through the intermediary of a threshold circuit denoted CS, and relative to a specific reference voltage denoted Vref, a pulse for triggering the electromagnetic clutch uoupling device 8, 9 so as to avoid successive rebounding of each percussion member Mi 15 after the calibrated impact is applied. It will be Poe understood, of course, that the sensor itself may be constituted by the sensor means Ci associated with the corresponding percussion means Mi, the signal delivered by each sensor Ci being compared with a reference value substantially corresponding to the peak value of the signal generated by the impact pulse. The pulse delivered by the threshold circuit CS then serves, I through the intermediary of the interface IF, to control *via the central processor unit UC the electromagnetic clutch coupling means in order to engage the latter, after a predetermined time-delay, in order to prevent any consequent rebound.

There has thus been described a method and a device for mechanical testing of civil engineering structure surfacings that offer particularly high performance. Use of the device as previousl, described, in particular with reference to the aforementioned figures 6 through 9, may advantageously be effected sequentially by the operator. A phase for mechanical initialisation of the device being provided first of c i i i i I WO 87/07378 PCT/FR87/00177

U

all, the plurality of sensor means Ci is first placed in position, the feet 17 of each of the latter being placed in contact with the ground by the operator. The control processor system previously described having been appropriately initialised, the mobile support 3 naturally being maintained stationary at the level of the spikes, the operator can then initiate the sequence of impulse ;npacts generated by each of the percussion means Mi in succession. The data or signatures corresponding to the test point Pi or Pij are then memorised in succession by the central processor unit UC and a first measurement sequence on a previously described alignment carried out; the operator can then move all of the device in the translation direction T, &see 15 and in particular the mobile support 3, so as to position the system for a new sequence, and so on. The S* distance of such displacement may Oe determined by the S" operator to produce a meshed array as previously described.

S. 20 The use of a device comprising three pairs of sensors Ci, percussion members Mi on a mobile support 3 has made it possible to test a motorway surfacing, the j duration of the operation for one kilometre, representing approximately 200 cast concrete slabs, having been 2.15 hours. The device and the method in accordance with the invention have thus made it possible to test motorway surfacings over a distance of 2.77 km in a working day of 6 hours.

o I r i ~L -i II

Claims

1. A method for mechanical testing of civil engineering structure surfacings, consisting in: establishing at least one signature of the response of a reference sound surfacing to an impulse impact, establishing a plurality of signatures of the response to an impulse impat of a surfacing of the same type in which reference sample defects have been formed, said signatures relating to the reference sound surfacing and to the surfacing comprising the sample defects constituting reference signatures, submitting a plurality of specific points on said surfacing to be tested to at least one impulse impact test in order to determine the signature of the impulse response at each of said specific points, comparing the impulse response signatures of said points to reference measurement signatures to establish an identification based on resemblance criteria.

2. A method according to claim 1, wherein said reference signatures and said measurement signatures are the responses to an impact pulse in a mobility-frequency diagram.

3. A method according to any one of the preceding claims, wherein the impact pulses for establishing the reference and measurement signatures are calibrated impact pulses.

4. A method according to any one of claims 1 to 3, wherein said measurement signatures are compared with said reference signatures by: comparing specific values of the mobility-frequency diagram of the measurement Signatures to corresponding values, referred to hereinafter as eigen values, of the reference signatures, calculating a correlation or resemblance coefficient enabling the aforementioned identification to be obtained. i- ~e 22 A method according to any one of claims 1 to 4, wherein said specific points at which said surfacing is subjected to at least one impulse impact test are distributed in a meshed array, the increment of the array being determined according to the resolution required.

6. A device for mechanical testing of civil engineering structure surfacings, comprising: a mobile support adapted to be moved across the surface of the surfacing, percussion means disposed on the support, said means serving to generate sequential calibrated impulse impacts on said surface of the surfacing, sensor means fastened to the mobile support, said sensor means being mechanically decoupled from the support, said sensor means serving to deliver an electrical signal representative of the impulse response of the surfacing to the calibrated test impacts, wherein the device further comprises device sequential control processing means and reference and measurement signature Sprocessing calculation means conforming to the method according to any one of claims 1 to 5, said control processing and calculation means comprising: a microcomputer provided with peripheral devices, said peripheral devices including: non-volatile memory means serving to memorise digital valuet representative of said I measurement signatures, electrically reprogrammable memory (EEPROM) type memory means in which are memorised digital values representative of the socmlled reference signatures, reprogrammable read only memory (REPROM) type memory means in which is memorised a program for computing and processing values to compare the measurement signatures with the reference signatures in order to establish an identification based on criteria of resemblance, input/output control (analogue-digital/digital.analogue) interfaces connected to the drive and control means for the percussion members and the sensing means.

7. A device according to claim 6, wherein the percussion means is constituted by a plurality of percussion members aligned on the mobile support, the resulting alignment being transverse to the direction of displacement of the support. i I, r 23

8. A device according to claim 7, wherein with each percussion member there is associated a sensor member, the set of sensor members constituting the sensor means.

9. A device according to any one of claims 6 to 8, wherein each percussion member comprises: a percussion head mounted at the end of an arm forming a lever arm and movable in rotation about an axis substantially parallel to said alignment, drive means for said arm serving, through an intermediary of the percussion head, to generate in succession a plurality of calibrated impacts. A device according to any one of claims 7 to 9, wherein said calibrated impacts consist in an impact pulse with an amplitude between 100 and 1000 daN and with a duration less than or equal to 1 ms.

11. A device according to claims 8 and 10, wherein the drive means for the arm *comprises: an electromagnetic clutch coupling device mechanically fastened to said arm forming a lever arm, rotational drive means for rotating said clutch, said rotational drive means and said clutch coupling device serving to displace the arm forming a lever and the percussion head into a calibrated impact armed position, return spring means mechanically fastened to the support and to the arm forming a lever arm, said return spring means and said clutch coupling device serving to displace i the arm forming a lever arm and the percussion head to a calibrated impact position.

12. A device according to any one of claims 6 to 11, wherein the sensor means comprises: S. a box forming a sensor means chassis which, in operation, is rendered mechanically fast with the mobile support through the intermediary of first decoupling spring means, a sensing head mechanically fastened to the box forming the chassis through the intermediary of second decoupling spring means. L .i i- _i i i 24

13. A device according to claim 12, wherein the sensing head comprises: a support lever arm pivoted to rotate about an axis fixed relative to the chassis, the opposite end of the lever arm being mechanically fastened to the chassis through the intermediary of said second decoupling spring means, F, sensing cell mechanically fastened to the lever arm through an intermediary of third decoupling spring means.

14. A device according to claim 13, wherein th sensing cell comprises: an electromechanical transducer of the accelerometer or geophone type, the sensitive surface of said transducer being mechanically fastened to a hard material spike adapted to be placed in contact with the measurement point on the surface of the surfacing. A device according to any one of claims 12 to 14, wherein the box forming the chassis comprises three support spikes adapted to come into contact with the surfacing.

16. A device according to claim 15, characterised in that said input/output control interfaces include a sensor responsive to the peak value of the calibrated impact amplitude, said sensor delivering through the intermediary of a threshold circuit a pulse to trigger the electromechanical clutch coupling device to prevent rebounding of each percussion member after application of a calibrated impact. C 1 0, •17. A method or device for mechanical testing of civil engineering structure surfacings substantially as hereinbefore described with reference to the accompanying drawings. *0' DATED this 5th day of July, 1990. CENTRE EXPERIMENTAL DE RECHERCHES ET D'ETUDES DU BATIMENT ET DES TRAVAUX PUBLICS. '4 ",*>OAD AUSTRALIA A-